Gardaí and officials from Monaghan County Council are investigating an illegal dump near Clones, Co Monaghan.
The eight-acre dump at Colemans' Island, found earlier this week, contains industrial and household waste, some of which has been traced to Munster.
The site had been under surveillance in an attempt to catch those dumping illegally, but gardaí have now decided to examine the waste to determine its origin.